The present invention relates to a suction gripping unit.
In the following description, specific reference is made purely by way of example to the cigarette packing sector, and in particular to a suction gripping unit for supplying blanks on a cigarette packing machine.
Cigarette packing machines are known to employ a suction gripping unit for feeding blanks successively between a blank pickup station, located at a blank store, and a supply station where the blanks are transferred to respective seats on a packing wheel.
Known suction gripping units such as those described in U.S. Pat. Nos. 4,513,957, 3,649,002 and 5,511,772 comprise a gripping head having a cavity connected through a conduit to a vacuum source and a valve for selectively interrupting the communication between the cavity and vacuum source. Some of the known units are also provided with venting holes for venting the cavity when the gripping head has to release the blank. The known units are not satisfactory when the blanks have to be transferred to a cigarette packing machine with an output close to twenty packets per second. For achieving that output the unit should permit a rapid alternation of vacuum and atmospheric pressure inside the cavity.
It is an object of the present invention to provide a suction gripping unit designed to eliminate the aforementioned drawbacks, and which in particular is cheap and easy to produce.
According to the present invention there is provided a suction gripping unit comprising at least a gripping head rotating about an axis and having at least one cavity defined in said suction head; suction means for creating a vacuum inside said cavity, said suction means comprising a conduit communicating with said cavity, a suction connected to said conduit and a control valve located between said pump and said cavity movable between an open position in which said cavity is in communication with the pump and in a closed position in which said valve interrupts the communication between the cavity and the pump; wherein the suction gripping unit comprises at least a venting hole in close proximity to the valve for automatically venting said cavity when said valve is in the closed position.